I tried this and they didn't want to touch, since it could void warranty.I have the GX 550 OT+ with the ML sound system. I will probably take it to my high quality local audio shop to see if they can add an underseat subwoofer and add/replace high quality speakers in the rear passenger doors or back, so that I can get a more enveloping sound as the driver. I like the ML sound (it's balanced, not "wow"), but dislike the "front stage only" approach when I'm driving solo. I'd prefer a more balanced front-to-back 'surround' than the ML was designed to give.